Securities - Summary of Securities Held for Investment and Securities Available for Sale (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Marketable Securities [Abstract]
Held for investment, at cost (fair value: $8,398 and $8,671, respectively)	$ 8,333	$ 8,593
Available for sale, at fair value	499,525	516,190
Total	$ 507,858	$ 524,783

Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

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